The separation of methanol transitions into two classes corresponds to different maser pumping mechanisms but not to the type of associated astronomical objects – Class I methanol masers have the collisional pumping mechanism, while Class II methanol masers are pumped by radiative excitation [1]}, [2]}. The Class I methanol masers trace shocked gas in star-forming regions, and the shocks may be attributed to different phenomena of star-formation as bipolar outflows or expanding H II regions [3]}. The interstellar shocks compress and heat up the gas, which is a conducive condition for the collisional pumping of Class I methanol masers. Here, we use the magnetohydrodynamic model of C-type shock wave published by [4]}, [5]} to study the collisional excitation of methanol and emergence of maser radiation. In this work we provide the list of methanol transitions that have population inversion in the post-shock region and may be observed as masers.
